Saturated hydrocarbon can be converted to unsaturated products such as acetylene and/or ethylene by pyrolysis reactions. One such pyrolysis reaction, steam cracking, can be used to produce acetylene and ethylene from hydrocarbon mixtures having a relatively broad molecular weight range, such as mixtures comprising hydrocarbon having a carbon number from about C2 to about C20, (e.g., ethane, naphtha, diesel, gas oil, etc.). Higher temperature pyrolysis, e.g., at a temperature ≧1200° C., can be used to produce acetylene and ethylene from methane.
Hydrocarbon source materials, e.g., crude oil and natural gas, generally have a significant heteroatom content, e.g., in the form of sulfur-containing, oxygen-containing, and nitrogen-containing molecules. In conventional pyrolysis processes, these are removed upstream of the pyrolysis in order to prevent contamination of the hydrocarbon product. This removal can be difficult to accomplish, particularly for sulfur-containing molecules when these are present in relatively high concentration. Some of the difficulties involved in removing sulfur-containing molecules upstream of pyrolysis result from the wide distribution of the molecules' molecular weights, chemical bonding characteristics, atmospheric boiling points, etc.
For sources of liquid hydrocarbon containing both hydrogen sulfide and mercaptan, two separations are generally required: a first separation for removing hydrogen sulfide, e.g., by stripping; and a second separation for removing mercaptans, e.g., by caustic extraction. For sources of hydrocarbon in the vapor phase, an amine contactor is generally utilized for removing hydrogen sulfide, with mercaptan being removed by caustic extraction. There is a need for improved pyrolysis processes having fewer sulfur-removal steps, particularly for processes that have the flexibility to locate the sulfur removal either upstream or downstream of the pyrolysis.